Foams are known to have widespread utility in hydrocarbon recovery applications. For example, Petroleum Abstracts of U.S. Pat Nos. 4,797,003 and 4,730,676 indicate that foams can be employed as downhole cements and as fracturing fluids, respectively. It is further known that foams have utility for conformance improvement treatments and mobility control in conjunction with oil displacement flooding of subterranean oil-bearing formations. Foams used for conformance improvement and mobility control are typically fine-textured foams that contain shear-sensitive polymers. The polymers have high molecular weights and long chain lengths which impart desirable properties to foams for the specific hydrocarbon recovery applications set forth above.
Conventional processes for generating foams typically combine a liquid stream and a gas stream at high velocity and subject the combined streams to an abrupt and extreme pressure drop across a valve, a choke, or even a wire mesh screen. While such a technique is effective for rapidly generating foams, it can have harmful consequences for the generation of oilfield foams, and particularly for the generation of foams containing shear-sensitive components in the liquid stream. The abrupt pressure drop used to generate the foam creates high shear forces that substantially degrade the polymer entrained within the liquid phase of the foaming fluid, thus, rendering the foam less effective for its intended use.
As such, a foam generator and method of operating the same are needed which do not substantially degrade the shear-sensitive components of a foam generated thereby. Accordingly, it is an object of the present invention to produce a finely-textured foam from shear-sensitive fluids which exhibits relatively little shear degradation. It is further an object of the present invention to provide a foam generator having a modifiable structural configuration which enables the operator to maintain the pressure drop across the generator within prescribed limits under variable operating conditions. It is yet another object of the present invention to provide a foam generator that is operable in such a manner as to avoid abrupt incremental pressure drops, yet achieves a minimum total pressure drop across the entire generator.